Geological and geochemical zoning of the Grasberg Igneous Complex, Irian Jaya, Indonesia

摘要: Abstract The Grasberg Igneous Complex is host to a porphyry CuAu deposit whose hypogene mineralization of remarkably high grade. complex occupies the central portion Ertsberg Mining District, in highlands New Guinea province Irian Jaya, Indonesia. Disseminated and stockwork confined intrusive rocks emplaced tightly folded carbonate strata Tertiary age. Mineralization extends from surface at 4,200 m elevation deepest drill penetrations 2,700 includes 700 million tonnes, mineable by open pit, an average grade 1.4 wt.% Cu 1.8 ppm Au. Two distinct stages spatially coincident intrusion produced two nested coaxial orebodies having significantly different styles as well sulfide-rich skarn margin igneous complex. their attendant have been radiometrically dated 2.7 3.3 Ma. earliest stage, Dalam Diatreme (DD), hosts deep, largely disseminated weak zone. highly fragmental, with clasts matrix both dioritic composition. chalcopyrite dominant has 1.2% 0.5 top mineralized zone lies 800 below present topographic surface. Based on occurrence volcaniclastic pyroclastic assemblages noted there, may be erosional remnant maar volcano. diatreme exhibits developed, sharply defined silicate zoning distinctive minor trace element signature. middle Main stock (MG), source intensely developed quartz magnetite dilational that carries veinlet-controlled mineralization. Grades averaging 1.5% 2 Au intersected core between 4200 2700 m, are expected continue depth. Rocks this stage non porphyritic monzodiorites. hosted MG which completely encloses it. Silicate alteration concentrically around MG, overprints earlier mineral phase. third final associated South Kali Dikes, was weakest mineralizing pulses. tabular, structurally controlled quartz-bearing monzonite body. It breaches originally continuous cylinder formed stages, resulting body low area outward into limestone southeast Complex. (SK) averages 0.3% 0.5% l early phase; phase barren. relatively short distances beyond contacts dikes, less intense than stronger phases Because its recent formation because rapid rates erosion, system suffered only structural dislocation, effects weathering extend shallow Supergene oxidation related clay upper 30 rocks. Copper enrichment chalcocite covellite rarely more 1.3 times original 100 pre-mining